Expanding projectiles may be used for increasing impact at a target point and may be useful for applications with reduced projectile speeds, for example with subsonic ammunition.
Subsonic ammunition is ammunition designed to operate at speeds less than the speed of sound, which at standard conditions is 343.2 m/s (1,126 ft/s). This avoids the supersonic shockwave or “crack” of a supersonic bullet, which particularly for suppressed or silenced firearms influences the loudness of the shot.
One way to accomplish effective bullet speeds below the speed of sound is to use a heavier bullet to reduce muzzle velocity below the speed of sound.